Mention that non-numeric host is allowed in API call if "dns" is used

doc/nghttpx.h2r

@@ -543,9 +543,9 @@ connections or requests.  It also avoids any process creation as is
 the case with hot swapping with signals.
 
 The one limitation is that only numeric IP address is allowd in
-:option:`backend <--backend>` in request body while non numeric
-hostname is allowed in command-line or configuration file is read
-using :option:`--conf`.
+:option:`backend <--backend>` in request body unless "dns" parameter
+is used while non numeric hostname is allowed in command-line or
+configuration file is read using :option:`--conf`.
 
 SEE ALSO
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